"Eating food rich in vitamins and minerals keeps the brain younger," reports the Daily Express. The headline was prompted by a US study of a new diet called MIND, which appeared to slow down ageing of the brain...

"Eating food rich in vitamins and minerals keeps the brain younger," reports the Daily Express. The headline was prompted by a US study of a new diet called MIND, which appeared to slow down ageing of the brain.

The MIND diet was developed specifically to help improve brain function and reduce dementia, and is a combination of the Mediterranean diet and the blood pressure-lowering DASH diet.

Both of these diets have previously shown positive effects on cognitive decline. The researchers wanted to see if they could narrow down which elements were the most important.

The MIND diet involves eating "brain-healthy" foods, with particular emphasis on eating berries, such as blueberries, and green leafy vegetables, like spinach.

Unlike DASH and Mediterranean diets, MIND does not require eating lots of fruit, dairy or potatoes, or eating more than one fish meal a week.

Among the MIND diet components are 10 "brain-healthy" foods:

green leafy vegetables, such as spinach and kale

other vegetables, such as red peppers, squash, carrots and broccoli

nuts

berries, including blueberries and strawberries

beans, lentils and soybeans

wholegrains

seafood

poultry

olive oil

wine (in moderation)

And five unhealthy foods:

red meats

butter and stick margarine

cheese

pastries and sweets

fried or fast food

Some 960 participants, with an average age of over 80, without dementia completed food questionnaires and brain function tests each year for an average of five years.

The study found those who stuck closely to the MIND diet had brains about eight years younger than those in the study who didn't.

While these results are encouraging, this type of study can only show an association between diet and improved brain function – it cannot prove causation. Even so, the study does lend weight to the potential benefits of eating this type of diet.

Dr Clare Walton, of the Alzheimer's Society, told the Mail Online: "Previous research suggests that the MIND diet can reduce the risk of developing dementia, and now we see it could also slow down the cognitive decline normally seen with age."

"It's important that people realise there are several steps you can take to reduce your risk of dementia, in addition to a healthy balanced diet, including being physically and mentally active and not smoking."

Where did the story come from?

The study was carried out by researchers from Rush University Medical Center in Chicago, and Harvard School of Public Health in Boston. It was funded by the National Institute on Aging.

The study was published in the peer-reviewed medical journal Alzheimer's and Dementia.

In general, the media reported the story accurately, but the study's limitations were not fully explained.

What kind of research was this?

This was an observational study that aimed to investigate the relationship between the Mediterranean-Dietary Approach to Systolic Hypertension (DASH) diet intervention for neurodegenerative delay (MIND) and its protective properties for cognitive decline seen with ageing.

The MIND diet is a combination of the Mediterranean and DASH (Dietary Approaches to Stop Hypertension) diets. Researchers say both diets have shown positive effects in delaying the decline in brain function in previously conducted randomised control trials.

A number of other studies have also observed slower decline in mental abilities with high consumption of vegetables and green leafy vegetables.

What did the research involve?

Older adults from Chicago were assessed annually between February 2004 and 2013 in terms of their diet and cognitive abilities. This comprised 960 residents of more than 40 retirement communities and senior public housing units. Their average age was 81.4 years, and 75% were female. Though the study spanned nine years, the average follow-up was 4.7 years.

The study participants did not have dementia at the time of enrolment into the trial and individuals with known dementia were excluded from the study.

Each participant underwent annual structured clinical evaluations and completed food frequency questionnaires, including total energy intake. The diets were scored according to how closely they followed the MIND diet.

Brain function testing was performed using 21 tests, 19 of which summarised ability in five areas:

Lastly, they used statistical methods to assess the relationship between the MIND diet and brain function score.

What were the basic results?

Higher MIND diet scores were associated with slower mental decline. This was true for all five mental tests, particularly for episodic memory, semantic memory and perceptual speed.

People with MIND diet scores in the top third had a slower decline than those in the bottom third, which was equivalent to being 7.5 years younger.

The results remained significant when potential outside factors (known as confounding factors) were taken into account, including hypertension, heart attack, stroke and diabetes.

How did the researchers interpret the results?

The researchers concluded that, "Higher MIND diet score was associated with slower decline in cognitive abilities". They said that, "The MIND diet was based on the dietary components of the Mediterranean and DASH diets, including emphasis on natural plant-based foods, and limited intake of animal and high saturated fat foods.

"However, the MIND diet uniquely specifies consumption of berries and green leafy vegetables, and does not specify high fruit consumption (both DASH and Mediterranean), high dairy (DASH), high potato consumption, or more than one fish meal per week (Mediterranean)."

Conclusion

This observational study aimed to investigate the relationship between the MIND diet and its protective properties for mental decline in an older population.

The study has several strengths, including the large sample size, long observational period of up to nine years, regular annual assessment of cognitive functions, and comprehensive assessment of diet.

However, one of the main limitations is that this type of study cannot show cause and effect – it can only show an association between the diet and slower mental decline. There may be other unmeasured factors that account for the results, such as genetics, other medical conditions or medication.

It also relies on self-reported estimates of dietary intake, so there is a chance for recall and reporting bias. Also, the study population at the time of enrolment was free of dementia, so we do not know how this diet would work in people with, or at increased risk of, dementia.